merely threw out this solution because he thought it easier to defend than one founded on corrections to the solar theory, and he adds that his calendar was not written for learned men, and would never be seen outside Styria.[1] It happened, however, that the calendar was read by Herwart von Hohenburg, who in January 1599 requested Kepler to give him further information about the solar eclipse. Being thus obliged to consider the matter more fully, Kepler did so in his reply, in which his wonderful genius displays itself by the way in which he suggests that the moon might be retarded in its motion by a force emanating from the sun, which would be greatest in winter, when the moon and earth are nearer to the sun than they are in the summer.[2] At the same time he suggests that the phenomenon might also be caused by an irregularity in the rotatory velocity of the earth, and in after years he accepted this idea, and did not consider the phenomenon as caused by an equation in the lunar motion.[3]
Tycho Brahe's discoveries as regards the lunar motion in latitude were as important as those he made of inequalities in longitude. The inclination of the lunar orbit to the ecliptic had by Hipparchus been found to be 5°, which value had been retained even by Copernicus. Several of the
- ↑ Ibid., pp. 409–411.
- ↑ Ibid., p. 412 et seq. Compare another letter from Kepler to Herwart of April 1599, published in Ungedruckte wissenschaftliche Correspondenz zwischen J. Kepler und H. von Hohenburg, 1599. Edirt von C. Anschütz. Prag (Altenburg, S. A.), 1886.
- ↑ This idea is particularly developed in Epitome Astr. Copern., Liber IV. (Opera, vi. pp. 359 et seq.). See also an interesting paper by Anschütz in Zeitschrift für Mathematik und Physik, Jahrgang xxxi. and xxxii., 1886–87. In this the author maintains that Tycho Brahe cannot be considered as the discoverer of the annual equation, because he did not distinctly announce it as a separate inequality like the variation, but allowed for the effect of it by leaving out part of the equation of time. I confess myself unable to follow this reasoning. Tycho clearly perceived the effect of the annual equation, and only adopted the peculiar dodge about the equation of time for fear of making his theory too complicated. We might as well deny that Columbus discovered America because he lived and died in the belief that he had merely come to the eastern extremity of Asia.
